1. Field of the Invention
The present invention relates to a tight, hermetic, miniature pyrotechnic priming device used in the formation of a pyrotechnic chain initiated by a high energy beam supplied by a laser source.
This type of pyrotechnic chain has mainly been developed for ballistic applications involving weight and volume problems linked with the number of pyrotechnic functions to be carried out.
The inventive pyrotechnic priming device is able in all cases to replace and optimize the hitherto used conventional pyrotechnic components for all and in particular high energy pyrotechnic applications.
A photopyrotechnic functional chain utilizing the light energy from a laser source as the stimulus for initiating pyrotechnic substances, which can be carried on ballistic missiles, is constituted by three main elements, namely a "laser station", an optical cable for carrying the light energy and a pyrotechnic component of the detonator or firing device type connected to the optical cable. The laser station essentially comprises a laser source, optical switches and a control logic. The laser source can operate in the triggered mode or in the relaxed mode.
The term "optical cable" is understood to mean both an optical fibre and a bundle of optical fibres. The term "pyrotechnic substance" is understood to mean primary explosives such as nitrides, fulminates, tetrazines, etc., secondary explosives such as PETN, RDX, HNS, etc., and pyrotechnic compositions such as igniting, illuminating, tracer, smoke producing and similar compositions.
The term "high energy" imposes the exclusive use of secondary explosives or pyrotechnic compositions, whose sensitivity thresholds to the different safety tests are equal to or below those of trimethylene nitro amine.
A pyrotechnic detonator is a device charged with primary and/or secondary explosives which can be initiated under the action of a laser beam and making it possible to obtain an adequate shockwave for initiating another pyrotechnic component charged with secondary explosive. The operating conditions of such a detonator is detonation. With respect to the pyrotechnic firing devices, they contain a pyrotechnic substance which can ignite when it receives an adequate heat supply, e.g. in the form of a laser beam, whereby said flame can lead to the firing of another pyrotechnic composition. The operating conditions of a firing device is combustion or deflagration.
The pyrotechnic device according to the invention constitutes both a detonator and a pyrotechnic firing device.
2. Brief Description of the Prior Art
Most presently known photopyrotechnic priming devices have a poor seal and/or hermiticity with respect to the exterior, which has two disadvantages. Firstly the pyrotechnic priming substance is poorly protected against external influences (moisture and varyingly corrosive atmosphere), which can be very prejudicial to its operation. Moreover, during the firing of the pyrotechnic charge, efficiency losses can occur as a result of gas leaks caused by the pyrotechnic charge during detonation, as well as risks of polluting surrounding equipment and in particular the "laser station".
Recently FR-A-2 615 609 has given consideration to a pyrotechnic priming device having a hollow body for receiving a pyrotechnic charge initiated by a laser beam, whose focussing is ensured with the aid of a truncated cone-shaped sapphire optics located in the body of the device. The fitting of said optics associated with a seal also protects the pyrotechnic charge against external influences. The construction of said optics also makes it possible for the same to withstand mechanical effects produced during the operation of the charge, so that there are no gas leaks through the passage provided for the laser beam.
Although this device solves a certain number of problems compared with the earlier devices, it still suffers from excessively large overall dimensions when it is to be used on ballistic missiles. In particular, the truncated cone-shaped optics is associated with one or two other lenses located at a relatively large distance from said optics and has relatively large diameters. Moreover, the sealing and/or hermiticity of said device are still inadequate.
The invention also relates to a miniature photopyrotechnic priming device having improved sealing and/or hermiticity compared with those of the prior art photopyrotechnic devices.
It is also known from FR-A-2 311 952 to maintain a lens in a hollow body with the aid of a thermoretractable plastics sheath. Such a thermoretractable sheath cannot be used in the pyrotechnic field. Thus, chemical incompatibility exists between the plastics sheath and the explosive products (the intermolecular migration can introduce a "desensitization" of the explosive, which may lead to non-detonation or non-deflagration). In the pyrotechnic field, a desensitizing substance is one which reduces the sensitivity of the explosive to shocks and friction.
Moreover, a thermoretractable sheath has a very limited thickness and leads to a problem of the resumption of the mechanical strength on the body, a sealing problem and a hermiticity problem which are not solved (cylindrical irregularity of the sheath, aging of the plastics material in particular use conditions and the sheath can slide with the vibrations). Finally, the fitting of a thermoretractable sheath needs a temperature rise up to 125.degree. C.